Thermomechanical fatigue of cast Ti Al alloy

Ti Al alloy has the advantages of high specific strength, specific rigidity, good high temperature oxidation resistance and creep resistance, and its density is only half of that of Ni based superalloy. It can be used in the low pressure turbine disc, turbine blade, transition tube beam, exhaust valve, nozzle and other parts of high thrust weight ratio and large culvert ratio aeroengine instead of Superalloy in the temperature range of 650 ℃ ~ 900 ℃. Ti Al alloy has been successfully applied in aeroengine, automobile and other fields in the United States and Europe, and it has also been identified as one of the preferred materials for developing 12-15 thrust weight ratio aeroengine in China.

Since the successful application of Ti Al alloy in the 6th and 7th stage blades of low pressure turbine of genx engine by GE company in 2007, there have been many successful applications of Ti Al alloy. More and more attention has been paid to the basic and applied research of Ti Al alloy by the international community. China in Ti The basic research of Al alloy, such as composition design, microstructure control and so on, has been at the leading level in the world, but the basic research on the mechanical behavior, service performance characterization and evaluation of Al alloy is still weak. Among them, the research on the mechanical thermal coupling behavior based on the service environment of engine, such as thermal mechanical fatigue (TMF), is less, and the accumulation of relevant performance data is insufficient, which can not effectively reflect The true service performance of alloy can not support the design and supply of components.

In the same research field, a lot of reports have been given abroad. For example, hjchrist et al. Studied the thermo mechanical fatigue behavior of xd47-2-2 alloy with two-state structure in the temperature range of 500 ℃ ~ 750 ℃, and obtained that the reverse phase (OP) showed higher damage, which is consistent with the research results of mroth and H Biermann. At the same time, most of the studies think that ti The microstructure evolution of Al alloy is similar to that of isothermal low cycle fatigue. V Bauer et al. Studied the thermo mechanical fatigue behavior of Bi state ti-47al-5.1nb alloy in the temperature range of 450 ℃ ~ 800 ℃. It was found that the average tensile stress existed in the process of reverse phase (OP) and the average compressive stress existed in the process of same phase (IP). They attributed the phenomenon to the periodic softening of the average stress at higher temperature and the periodic hardening at lower temperature.

Different from the previous study of uniaxial load, SP Brookes et al. Reported the axial torsional load condition of ti-45al-5nb alloy with near γ structure and the thermo mechanical fatigue behavior in the temperature range of 500 ℃ ~ 750 ℃. Compared with the uniaxial and single torsional load, the thermo mechanical fatigue of this multi axial load condition shows a lower life. In China, the Institute of metals of the Chinese Academy of Sciences has made a preliminary study on the thermo mechanical fatigue behavior of ti-46.5al-5nb alloy in the temperature range of 200 ℃ ~ 600 ℃ and 300 ℃ ~ 700 ℃, revealing that the fatigue life of trapezoidal wave is higher than that of triangular wave under the same conditions, but the data obtained is limited.

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